Numerous types of cocatalysts for metallocene-catalyzed olefin polymerizations are known. These include various aluminoxanes, and alkyl and aryl boranes and borates. Such cocatalysts function by forming and stabilizing cationic metallocene and related complexes of the early transition metals, e.g., titanium, zirconium, and hafnium.
These cationic metal complexes are very reactive towards electron donating centers. Anionic complexes with alkoxide ligands can provide sites at the alkoxy oxygen atoms for reaction with the metal cationic species and thereby a mechanism for decomposition of the cation-anion complex.
The synthesis of the Li.sup.+ derivative of the Al(OC(Ph)(CF.sub.3).sub.2).sub.4 !.sup.- complex and its use as a catalyst for 1,4 conjugate additions has been published in Organometallics, 1996, 15, 3776. In these catalytic reactions, it is the Li.sup.+ that is the catalytically active species. The Al(OC(Ph)(CF.sub.3).sub.2).sub.4 !.sup.- anion is a weakly coordinating anion to the Li.sup.+ and imparts hydrocarbon solubility. No other metal species is used.
In a brief survey of the open and patent literature, the present inventors have not come across any specific reference to anionic species with alkoxy ligands, specifically aluminates and borates being used as cocatalysts for olefin polymerization. Generic formulas can encompass the alkoxy aluminates and borates, but all specific examples are for alkyl or aryl aluminates and borates. For example, U.S. Pat. No. 5,407,882 mentions aluminates, but the compounds cited in the description section and in the Examples in this patent document are all aryl and substituted aryl derivatives. In U.S. Pat. Nos. 5,198,401, 5,241,025, 5,408,017, and 5,470,927, generic formulas are given that could be envisioned by hindsight as encompassing the alkoxy aluminates, but specific references to aluminates of any kind are not given. In U.S. Pat. No. 5,241,025, neutral aluminum species of the type AlR.sub.3, where R includes alkoxy groups, are described. The function of these complexes is to act as scavengers for impurities in the polymerization reaction medium, not as activator cocatalysts.